[mlir][linalg] Update Linalg.md (NFC).

[gysit]

Summary

Update the paragraph on generic / indexed_generic to reflect the unification of these operations.

mlir/docs/Dialects/Linalg.md

2.  a "shape-only" tensor output value whose underlying elements are not used in
     information to lower levels of abstraction. In the future this will be
     replaced by an appropriate shape type when it is available as a builtin type
     (see the discourse discussion
     [Linalg and Shapes](https://llvm.discourse.group/t/linalg-and-shapes/2421)
     for more details).
 
 ### Payload-Carrying Ops<a name="payload_ops"></a>
 
-Linalg defines two payload carrying operations that implement the
-[structured ops](https://docs.google.com/presentation/d/1P-j1GrH6Q5gLBjao0afQ-GfvcAeF-QU4GXXeSy0eJ9I/edit#slide=id.p)
-abstraction on tensors and buffers. This is architected as two generic
-operations `linalg.generic` (resp. `linalg.indexed_generic`) that can express
-custom operations with *index-free semantics* (resp. *indexing semantics*). The
-properties of these generic ops are the result of applying the guiding
-principles described in the
-[Rationale Document](../Rationale/RationaleLinalgDialect.md). They are listed
-next, with a brief example and discussion for each.
+Linalg defines a payload carrying operation that implements the
+[structured op](https://docs.google.com/presentation/d/1P-j1GrH6Q5gLBjao0afQ-GfvcAeF-QU4GXXeSy0eJ9I/edit#slide=id.p)
+abstraction on tensors and buffers. This `linalg.generic` operation can express
+custom operations that optionally have *indexing semantics* (by accessing the
+iteration indices using the `linalg.index` operation). The properties of
+`linalg.generic` are the result of applying the guiding principles described in
+the [Rationale Document](../Rationale/RationaleLinalgDialect.md). They are
+listed next, with a brief example and discussion for each.
 
 #### Property 1: Input and Output Operands Define The Iteration Space<a name="prop1"></a>
 
 A `linalg.generic` op fully *derives* the specification of its iteration space
 from its operands. The property enforces that a localized IR element (the op)
 *has* all the information needed to synthesize the control-flow required to
 iterate over its operands, according to their type. This notion of IR
 localization bears some resemblance to
void batchmatmul::regionBuilder(ArrayRef<BlockArgument> args) {
   Value _5 = std_addf(_2, _4);
   (linalg_yield(ValueRange{ _5 }));
 }
 ```
 
 ### YAML Based Named Structured Ops
 
 Linalg provides a declarative generation tool (`mlir-linalg-ods-yaml-gen`) to
-automatically produce named ops from a YAML-based op description format
-intended to capture the structure of the named ops and be generated from a
-higher level "mathy" DSL syntax. This facility is currently in flight and is
-intended to subsume the above when ready. See the C++ class to YAML mapping
-traits in `mlir-mlinalg-ods-yaml-gen.cpp` as the source of truth for the schema.
+automatically produce named ops from a YAML-based op description format intended
+to capture the structure of the named ops and be generated from a higher level
+"mathy" DSL syntax. This facility is currently in flight and is intended to
+subsume the above when ready. See the C++ class to YAML mapping traits in
+`mlir-mlinalg-ods-yaml-gen.cpp` as the source of truth for the schema.
 
 Most of the above documentation roughly applies to this path and will be ported
 as migration continues.
 
 ## Open Issues and Design Alternatives<a name="open_issues"></a>
 
 Multiple open issues and design alternatives are in flight and it is time to lay
 them out for the community to discuss and pick apart: